The ratio of the moment of inertia about the neutral axis to the distance of the most distant point of the section from the neutral axis is called:
Try it first: pick an option, then read the explanation.
Correct answer: B. section modulus
Asked in SSC JE 01/03/2017 (Morning)
Detailed Explanation
Several "moduli" appear in strength of materials. Each is defined differently.
Why “section modulus” Is Correct
I divided by y_max is the section modulus Z. The bending stress at the extreme fibre is then simply M/Z.
| Term | Definition |
|---|---|
| Section modulus Z | I / y_max (bending) |
| Polar modulus Zp | J / R (torsion) |
| Modulus of rupture | Bending stress at failure, M_fail/Z |
| Flexural rigidity | E × I |
Why the Other Options Are Wrong
- A. polar modulus: Polar modulus = J/R, used in torsion.
- C. modulus of rupture: Modulus of rupture is a stress — the bending strength at failure.
- D. flexural rigidity: Flexural rigidity is the product EI.
Key Point
Z = I/y_max (section modulus).
Key Concepts for Students
- Rectangle Z = bd²/6, circle πd³/32.
- Modulus of rupture is used for concrete flexural strength (0.7√fck).
- Zp = πd³/16 for a solid shaft.
Practice more: this is question 37 in Bending and Shear Stress MCQs – Part 3. Try the whole set and check every answer instantly.